1. Field of the Invention
The present invention relates in general to a method and an apparatus for optically measuring or determining electric and magnetic quantities, and more particularly to improved method and apparatus adapted to measure an AC electric field or a voltage which produces the AC electric field, an AC magnetic field or an electric current which produces the AC magnetic field, and an electric power together with these quantities, by utilizing polarization of a light beam.
2. Discussion of the Prior Art
Recently, techniques utilizing the electrooptical effect or the Pockel's effect and the magnetooptical effect or the Faraday effect are drawing attention of the industries concerned with the art of measuring or determining electric and magnetic quantities or amounts such as a voltage or an electric field, an electric current or a magnetic field, and/or an electric power. These techniques use a beam of light as a medium for the measurement, and consequently assure a high degree of insulation from electromagnetic induction noises. This feature of the optical measuring method has been widely utilized in the field of electricity, for measuring the electric/magnetic quantities associated with power cables, electric wirings and other electric parts.
Such optical measurements of electric and/or magnetic quantities by utilizing a light beam may be effected by an apparatus, so-called, an optical sensor. For example, there are known an optical sensor for detecting a voltage (an electric field strength) by using the Pockel's effect, and a sensor for detecting an optical sensor for detecting an electric current (a magnetic field strength) by using the Faraday effect. However, either of these optical sensors is capable of detecting only one of these two quantities, voltage or current.
On the other hand, laid-open Publication Nos. 58-99761 and 59-50369 of unexamined Japanese Patent Applications propose an optical apparatus which uses a single optical sensor capable of measuring both a voltage (electric field strength) and a current (magnetic field strength). Described more specifically, the optical sensing apparatus for detecting the strengths of an electric field and a magnetic field, as disclosed in the Publication No. 58-99761, employs an optical material which exhibits both the Pockel's effect and the Faraday effect. This optical material is exposed to two light beams such that these two light beams are transmitted through the optical material, in respective directions which are perpendicular to each other. The strength of an electric field to which the optical material is exposed is measured based on the Pockel's effect of the optical material, while the strength of a magnetic field to which the material is exposed is measured by means of the Faraday effect of the material. The optical sensing apparatus for detecting the electric quantities, as disclosed in the Publication No. 59-50369,employs two light sources which emit respective light beams which are transmitted through respective Pockel's-effect element (an optical material exhibiting the Pockel's effect) and Faraday-effect element (an optical material exhibiting the Faraday effect). The Pockel's-effect element and the Faraday-effect element produce optical output signals indicative of different wavelengths. The amounts of current and voltage applied to the elements are measured based on the intensities of the optical output signals.
An optical apparatus for detecting an electric power is disclosed in laid-open Publication No. 61-172069 of unexamined Japanese Patent Application, wherein a light beam produced by a suitable light source is transmitted through a polarizer, and a Pockel's-effect element and a Faraday-effect element which are arranged in series. The light beam which has been transmitted through these two elements is incident upon an analyzer, which divides the transmitted beam into two components. These two components of the modulated light beam are received by respective two light-sensitive elements, which convert the received optical signals into equivalent electric signals. This apparatus determines the amount of AC electric power applied to the Pockel's- and Faraday-effect elements, based on the Pockel's and Faraday effects given to the incident light beam.
Thus, the conventional optical sensors are relatively complicated in construction. Namely, the conventional sensors for effecting simultaneous measurements of a voltage and a curent, use two light sources or two light beams, which lead to a relatively large number of optical components of the sensing head, resulting in a considerably complicated sensing system as a whole. Similarly, the conventional optical sensor for measuring the amount of electric power is complicated because of the use of two light-sensitive elements for receiving two components of an optically modulated light beam.